Version 10 of Tcl in comparison

Richard Suchenwirth 2002-12-16 - For people experienced in other languages, it may be interesting to compare code snippets between Tcl and other languages, to demonstrate similarities and differences. Please add more from your experience!

 void countdown(int n) {         | proc countdown {n} {
    int i;                       |
    for(i=n; i>0; i--) {         |    for {set i $n} {$i>0} {incr i -1} {
       printf("%d...\n", i);     |        puts $i...
    }                            |    }
 }                               | }

Everything is a command in Tcl. Function definitions are done with the proc command, assignments with the set command, in/decrementation of integers with the incr command.
Retrieving the value of a variable goes with prefixed $ sign - while mentioning the name of a variable it is not used
Variable type rarely matters and is not declared. Only incr would complain if its first argument is not an integer
Formatting values into strings goes in simple cases by straight string concatenation like in $i.... for stronger control, format is comparable to sprintf
puts, unlike printf(), needs no explicit newline.

Scheme

 (define foo 42)                 | set foo 42
 (define (square x) (* x x))     | proc square x {expr $x * $x}
 (define bar (square foo))       | set bar [square $foo]
 (define grill '(square foo))    | set grill {square $foo}

Functions are also defined with the proc command. Their result is the last executed command in the body
Arithmetics is not done with prefix functions, but Infix-style like in C, in the argument(s) to the expr command
set is used for variables, proc for functions - no unified define in Tcl (except if you write one - see the Scheme page ;-)
Tcl commands on toplevel are not enclosed in parens. Embedded commands like the first call to square go into brackets for eager evaluation; the equivalent to quoting is curly braces around a string

 (define (abs x)                 | proc abs x {
   (cond ((> x 0) x)             |    expr { $x > 0?  $x :
         ((= x 0) 0)             |           $x == 0? 0 :
         ((< x 0) (- x))))       |           $x < 0?  -$x}
                                 | }
                                 | or: proc abs x {expr abs($x)}

expr can, with the ?: operator, operate like cond
It also has built-in math functions that can be exported in a one-liner as shown (Importing expr functions)
Tcl needs less parens (which often amount to braces or brackets)

Tcl and other languages